Optical fingerprint acquisition

ABSTRACT

A swept distance between a subject and a plurality of cameras provides a plurality of raw images. Focused portions of the raw images are fused to generate a synthetic image and a distance image. A projection of the synthetic image and the distance image yields a panoramic image.

BACKGROUND

Current methods and systems for fingerprint acquisition are inadequate.Existing technology requires physical contact between the subject beingfingerprinted and the fingerprinting device. Physical contact with thedevice can pose a hygienic challenge which, for example, may requireperiodic cleaning of a surface or sensor to mitigate.

In addition, the quality of the acquisition depends on the experience ofthe person performing the fingerprinting. For example, if the subject'sfinger is not precisely rolled over the card or sensor pad, then imagequality is poor. As such, a subject or operator can manipulate theresults obtained using existing technology. Furthermore, existingtechnology is labor and time intensive and thus unsuitable for massprocessing facilities such as at an immigration checkpoint or at anairport.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 includes a pictorial representation of data collection andprocessing according to an example embodiment.

FIGS. 2A, 2B, and 2C illustrate a camera and a subject according to anexample embodiment.

FIG. 3 includes a view of a slice taken through a finger according to anexample embodiment.

FIG. 4 includes convergent beams directed to a subject according to anexample embodiment.

FIG. 5 illustrates a block diagram of a system according to an exampleembodiment.

FIG. 6. illustrates a flow chart for a method according to an exampleembodiment.

DETAILED DESCRIPTION

FIG. 1 includes a pictorial representation of data collection andprocessing. The figure includes example system 100A for acquiring andprocessing data. The figure also illustrates sample results for imagesassociated with touchless fingerprint acquisition.

According to one example, system 100A includes cameras 60A, 60B, and60C. Cameras 60A, 60B, and 60C are directed at subject 50A within volume55 and are coupled to processor 70A.

Volume 55 can include a chamber for receiving a finger or other subjectfor identification.

In particular, camera 60A is directed to subject 50A with a viewingangle aligned on radial 65A. In a similar manner, subject 50A is alsoviewed along radials 65B and 65C using camera 60B and camera 60C,respectively. Radials 65A, 65B, and 65C radiate from the center ofvolume 55 in which the subject is a target. The number of viewing anglesis selected to provide a meaningful perspective as to subject 50A and,in various examples, includes more or fewer than three cameras. Inaddition, the selection of the viewing angles can be tailored to theparticular subject of interest. In one example, the radials are selectedfor equal spacing between the cameras; however, in other examples, theradials are selected to provide a non-uniform distribution about thesubject.

In one example, cameras 60A, 60B, and 60C have a fixed focal length anda fixed depth of focus (sometimes referred to as DOF). Depth of focusrefers to the image-side depth and, in the context of a film-basedphotographic camera, is a measurement of how much distance exists behindthe lens in which the film plane remains in focus. Depth of field, onthe other hand, refers to the opposite side of the lens and is ameasurement of depth of acceptable sharpness in the object (or subject)space.

In capturing an image of three-dimensional subject 50A, such as afinger, multiple images are acquired. The multiple images are taken atdifferent distances relative to the subject. In one example, cameras60A, 60B, and 60C have a varying distance to the subject 50A. In oneexample, the distances are varied by a sweeping motion of subject 50Awithin volume 55, while cameras 60A, 60B, and 60C remain in a fixedlocation.

A light source can be provided for illuminating the subject 50A. Thelight source can include one or more discrete lighting elements that maybe located within volume 55 or a lighting element can be attached to orbuilt-in one or more of cameras 60A, 60B, and 60C. In one example, alight source and cameras 60A, 60B, and 60C are affixed to a frame orother structure.

In the example illustrated, processor 70A is configured to receive datafrom cameras 60A, 60B, and 60C.

Sequences 80A, 80B, and 80C depict a series of sample images taken atvarious distances and acquired using cameras 60A, 60B, and 60C,respectively. Sequence 80A includes raw images 81A, 82A, and 83A;sequence 80B includes raw images 81B, 82B, and 83B; and sequence 80Cincludes raw images 81C, 82C, and 83C. The raw images represent subject50A as viewed along different radials and taken at different distances.In this example, three radials are selected and three distances aredepicted; however, more or fewer radials and distances are alsocontemplated.

For the example illustrated, the outer profile of subject 50A appears inthe raw images. For instance, when viewed along radial 65A, subject 50Ayields profile 85. In a similar manner, profile 86 and profile 87 areshown for views taken along radials 65B and 65C, respectively.

A raw image includes a focused portion and an unfocused portion. Thelocation of the focused portion is determined by the distance betweenthe particular camera 60A, 60B, or 60C and the subject 50A.

Consider next the raw images of sequence 80A. When viewed at variousdistances, raw image 81A depicts focused portion 88, raw image 82Adepicts focused portion 89, and raw image 83A depicts focused portion90.

As illustrated in example image 82A, the focused portion 89 (focusedregion or patch) for a raw image can be identified by computingcontrast. A more sharply focused portion of an image will have highercontrast than other portions of the same image. A variety of algorithmscan be used to derive a measure of contrast. In one example, processor70A executes an algorithm to calculate contrast for different portionsof an image using per pixel luminescence. Other measures of contrast canalso be used, including those that include calculating a mean or medianluminescence and comparing with a factor based on a standard deviationfor the image. A measure of contrast can be based on a calculationderived from a single image or based on a calculation derived from aplurality of images in a sequence of images.

The sample images shown in FIG. 1 depict non-overlapping focusedportions in successive images. In other words, the focused portions ofthe various images do not overlap. In one example, the focused portionsof the various images overlap.

According to an example of the present system, the focused portions ofthe raw images are processed using a method known as fusion. Fusionrefers to combining selected portions from multiple images to form asingle, evenly focused image. In one example, the selected portions arethe focused portions corresponding to different planes of the subject.The different planes of the subject, or slices, are a product of thenarrow depth of focus and the relatively thick subject.

Various methods can be used for image fusion and they can be broadlyclassified as spatial domain fusion and transform domain fusion. Onemethod for image fusion uses overlapping focused portions and includescalculating correlation values for the various images.

The various images of the finger may move across the array of camerasensors as the finger moves relative to the camera assembly. Throughimage fusion, the various images are combined to render a single image.

As illustrated in the figure, the raw images of sequence 80A are fusedto form data 110A corresponding to radial 65A. Data 110A includessynthetic image 111A and distance image 112A. Synthetic image 111Arepresents a fusion of the various focused portions 88, 89, and 90.Distance image 112A represents a per pixel distance between subject 50Aand camera 60A. In one example, distance image 112A includes agray-scale representation with lighter regions corresponding to nearerdistances and darker regions corresponding to farther distances.

The raw images of sequence 80B are used to generate data 110B and theraw images of sequence 80C are used to generate data 110C. Data 110Bincludes synthetic image 111B and distance image 112B and data 110Cincludes synthetic image 111C and distance image 112C.

When fusing the raw images of the finger pattern, the system alsoacquires information corresponding to the distance or depth profile ofthe finger bulb. The finger bulb refers to the pad portion of the lastjoint of a finger or thumb. In one example, the narrow depth of focusallows acquisition of distance information for a slice. In one example,the distance information is acquired based on the relatively steepGaussian-like curve of contrast change with distance.

Image processing of the sequence of raw images yields a synthetic image(including the finger pattern details in sharp relief regardless of thefinger size and finger placement within a particular volume) and acorresponding distance image based on the depth profile.

The synthetic images 111A, 111B, and 111C and distance images 112A,112B, and 112C are stitched together to form panoramic image 120.

Image stitching refers to an image processing method for combiningmultiple images to produce a single image having a field of view that isgreater than one of the combined images. Stitching can include imageregistration and image blending.

Panoramic image 120 includes profile 122 having image details 124 whichcan include, for example, an arch, a loop, a whorl, or other featurethat corresponds with a rolled fingerprint image. Panoramic image 120represents a particular projection of the synthetic images and distanceimages.

A projection is a method of representing a curved body (such as a fingeror other subject) on a two-dimensional plane. A variety of projectionscan be generated based on the same set of synthetic images and distanceimages. For example, one projection can treat the finger as a cylinderand another can treat the finger as an ellipsoid. Other projections canalso be used. For example, one projection can reflect the distortioncaused by rolling a physical finger on a surface and another projectioncan reflect the same finger without distortion caused by the compressiveforces.

The panoramic image can represent a camera view looking from theperimeter of a circle toward its center and record both the optical dataand depth data.

FIGS. 2A, 2B, and 2C illustrate a camera and a subject. In FIG. 2A,camera 60D is directed at subject 50B along a viewing angle described asradial 65D. In similar manner, FIG. 2B illustrates camera 60E directedat subject 50C along a viewing angle described as radial 65E. Accordingto one example, the focused portion of a raw image (such as raw image82A) is determined by the distance between the camera and the subject.

In FIG. 2A, the distance is varied by moving subject 50B in a mannershown by arrow 20A while the position of camera 60D remains fixed. InFIG. 2B, the distance is varied by moving camera 60E in a manner shownby arrow 20B while the position of subject 50C remains fixed.

FIG. 2C illustrates camera 60F and subject 50G. A surface of subject 50Ghas a three dimensional curvature. Assume, for example, that camera 60Fhas a fixed focal length corresponding to the distance shown on radial65G. As such, the image lying within the depth of field for the cameralens, denoted by slice 30B, will appear focused and the details depictedin slice 30A and slice 30C will remain out of focus. The distance can bechanged by moving either or both of the subject 50G and camera 60F inorder to select a different slice.

In one example, the optics of camera 60F have a narrow depth of fieldrelative to the thickness or depth of the subject (such as a finger). Asynthetic image having a relatively large depth of focus can begenerated by fusing portions of a number of raw images in which the rawimages have a narrow depth of focus. The raw images are generated byincrementally sweeping the distance between subject 50G and camera 60F.By changing a distance between the camera and the finger, differentportions of the finger are in focus in the various raw images.

One example of the present system tolerates a wide variation in the sizeof the finger bulb. For example, the radius of the finger bulb arc of ayouth may differ in size from that of a mature bodybuilder by 5 mm ormore.

In one example, the depth of focus for the camera optics spans thepossible size variation and field of view (FOV) of a strip with a widthof about a third of the bulb. Since the depth of focus is directlyproportional to the f-number of the optical system, the larger the depthof focus, the more intense illumination or longer exposure time that isrequired in order to get a well-exposed image.

The present system generates a synthetic image having a large depth offocus by fusing a number of short depth of focus images. One example ofthe present system is immune to the relative finger-camera velocities upto approximately 100 mm/s. Cameras 60A, 60B, and 60C have a short depthof focus resulting from small f-numbers, which improves the amount oflight collected during 0.1 ms exposures.

As shown in the example of FIG. 2C, the attainable depth of focus(represented by slices 30A, 30B, and 30C) per image captured by camera60F is narrow. In one example, the depth of focus is approximately 1 to2 mm. Since a typical finger bulb is not planar but curves away from thecamera over 10 or so millimeters, a single image will not be in focusover its entire sector of the bulb. Any specific image will include awell-focused slice of the bulb pattern within the depth of focus, andother portions of the image will be out of focus and blurred.

In one example, the finger distance is varied so that the slicesoverlap. The portions of a raw image that are in focus are identified,extracted, and then computationally fused together into a single imagein which the whole bulb is sharp and appears to be taken by a camerawith a large depth of focus.

FIG. 3 includes a perspective view of an optical slice taken through ahuman finger using camera 60F. In the figure, subject 50E is depicted asa human finger. In this example, the focal length of camera 60F isconfigured to select a slice 140 which includes detail 145. Otherdetails as to a fingerprint on subject 50E can be brought into (or outof) focus by changing the distance between subject 50E and camera 60F.

In addition to determining distance based on focus as described earlier,one example uses structured beams of light arranged in a fixed pattern.The beams of light are projected in a fixed pattern onto the finger bulbto create bright dots on the finger surface. The convergent arrangementof beams causes the dot pattern to change with the finger distance, andthe dot pattern distortion provides coarse information on the bulbsurface 3D profile.

FIG. 4 illustrates an example in which light from convergent beams isdirected to subject 50F. Light from convergent beam source 410A andsource 410B is directed at subject 50F. Subject 50F represents a humanfinger, and for clarity, includes fingernail 49. A parameter associatedwith the convergent beams can be used to determine a distance. In theexample illustrated, the measured parameter includes distance 430 acrossilluminated region 420 at the surface of subject 50F. The convergentbeams are directed at included angle θ. Other methods can also be usedin determining the distance between the subject 50F and the camera.

FIG. 5 illustrates a block diagram of system 500 according to oneexample. System 500 includes processor 70B coupled to optical portion510. Optical portion 510 can include, in various combinations, aplurality of cameras (or one camera and a plurality of mirrors), light,a registration marking light source, and a convergent beam light source.Processor 70B is also coupled to network 520. Network 520 can include adigital communication network or an analog communication network such asa wide area or local area network. Network 520 can include wired andwireless components, and in one example, includes the Internet.Processor 70B is configured to communicate with machine-readable medium530. In various examples, machine-readable medium 530 can include amemory device, a signal communicated using a network, or other storagefor executing a programmed method. Processor 70B is coupled to I/O 540.I/O 540 can include a personal computer, a printer, a display, akeyboard, or other device for rendering (output) or entering (input)data or instructions.

An illumination source, such as source 410A and source 410B, can becontrolled by processor 70B or by I/O 540.

FIG. 6. illustrates a flow chart for method 600 according to oneexample. At 605, method 600 includes setting a value of distancevariable to value D. At 610, method 600 includes acquiring an image ofthe subject at a distance equal to value D. At 615, the raw image (at adistance equal to value D) and value D is stored in a memory. The rawimage and the value can be stored in a memory accessible to processor70B.

At 620, value D is shifted to the next value. Value D can be configuredto be incremented or decremented. At 625, a query is presented todetermine if data (including images and distance values) for alldistances have been acquired. If answered in the negative, then method600 continues by returning to acquire an image at 610. If the results ofthe query at 625 are in the affirmative, then method 600 continues, at630, with extracting focused portions from the raw images. At 635, thesynthetic image is generated by fusing the focused portions. At 640, thedistance image is generated using the distance information. At 645, apanoramic image is generated using the synthetic image and the distanceimage for a particular radial.

In one example, the panoramic image format has an image point density ofeither 500 or 1000 pixels per inch (ppi). One standard for roll-fingerimages provides that the image cover at least 80% of the finger arc,connecting the opposite nail edges. Since the sensor arrays of cameras60A, 60B, and 60C are planar, one approach for obtaining a panoramicimage includes stitching together planar images taken from two or more(for example, three or five) different angles. In one example, imagefusion is used to generate a reasonable depth of focus. Also, forreasons of geometric accuracy, the raw images may be corrected formagnification and projection errors.

One example of the present system has a resolution of 500 ppi. Thisresolution translates to a pixel density in the object plane of about 20pix/mm (the pixel pitch in the plane is 0.05 mm). An image exposure timeof 1 ms permits the system to operate at a relative velocity up to 100nm/s. The exposure time can be reduced by increasing illumination or byadjusting the optic system f-number.

Consider an example in which the finger is moving approximately towardthe cameras (or vice versa). Precise direction and velocity of thefinger in the volume is irrelevant and may differ in various scanningevents.

For this example, consider that volume 55 (FIG. 1) is 30 mm deep and thedepth of focus is 2 mm. The sharp areas in successive images areconfigured to overlap in order to enable fusion. In one example, theoverlap is approximately 25% and each slice will add (1−0.25)×2=1.5 mmof new coverage. To cover the whole volume, the camera acquires30/1.5=20 frames. Of those 20 frames, some will be largely blurred andcan be discarded before fusing.

Moving at a velocity of 100 mm/s, the finger travels 1.5 mm in 15 ms, soshooting the whole sequence will take 20×15=300 ms. As such, the camerasoperate at 66.6 frames per second. Other cameras having differentperformance can be used, which may allow extending both the maximumvelocity and the size of volume 55.

Lowering the relative velocity while retaining the high frame rate willresult in larger slice overlaps and hence a larger number of images dueto increased redundancy. The relative motion can be produced by sweepingthe finger through volume 55 or by moving the camera assembly toward amore or less stationary finger.

The panoramic image can include a projection from the center onto theinner surface of an inner cylinder. The inner cylinder axis isapproximately aligned with the finger axis. According to one example, anilluminator is approximately coaxial with the camera axis in order toobtain finger pattern images having good contrast and low geometricdistortion caused by shadows cast by the finger pattern ridges.

The illuminator can be coaxial with the camera. A panoramic image can beexpressed in cylindrical coordinates. As such, a pixel of the panoramicimage represents the intensity of the light reflected from the subjectand records the subject depth (distance to the subject from theperimeter).

According to one example, the panoramic image is generated from threesynthetic images and three distance images. A distance image representsthe depth (or distance) associated with the various focused portions inthe sequence of raw images. One example recovers the depth informationand thus the finger bulb shape.

One example includes a method for standoff (or touchless) capture of afingerprint image that is free of pressure-induced distortion caused bythe typical ink pad and paper method.

Additional processing using the panoramic image, the synthetic images,or distance images can generate any of a number of selected projectionsof the data.

In one example, visible spectrum light is used to acquire images withina range of distances. In the context of fingerprint capture, a workingdistance can be between approximately a few and a few tens ofcentimeters from the subject to the optical elements.

In one example, a registration mark is used to facilitate fusing orstitching of the various images. A registration mark can be a pixel-sizespot that is projected onto the surface of the subject. A projector can,for example, illuminate a small region without adversely affecting theresulting image quality. At 15 pixels/mm, a marker spot can be a coupleof pixels wide or approximately 0.1 mm in diameter. In one example, theprojector is integrated with the camera and controlled by processor 70B.

One example includes a system having a plurality of cameras and aprocessor. The plurality of cameras are configured to generate aplurality of raw images of a subject in a volume. The cameras have afixed focal length and a fixed depth of focus that is substantially lessthan a thickness of the subject. The cameras are directed along selectedradials with respect to a volume. A distance between a camera and thesubject is variable. A raw image includes a focused portion of thesubject corresponding to the distance. The focused portion is determinedby the focal length and determined by the depth of focus.

The processor is coupled to the plurality of cameras. The processor isconfigured to execute a set of instructions to generate a panoramicimage. The panoramic image is based on a plurality of synthetic imagesand based on a plurality of distance images. For a particular radial, aparticular synthetic image includes a fusion of a plurality of focusedportions. Also for that particular radial, a distance image is based onthe distance between the camera and the subject.

In one example, at least one camera remains stationary and the subjectis mobile and in another example, at least one camera is mobile and thesubject is stationary. Optionally, at least one camera is configured togenerate a time series of raw images. In one example, the processor isconfigured to generate a particular synthetic image using the raw imagesand a measure of contrast. In one example, the processor is configuredto communicate using a digital network.

One example includes a method. For at least two radials from a volume,the method includes receiving a sequence of acquired imagesdifferentiated in a distance from a camera to a subject within thevolume. The camera has a fixed focal length and a fixed depth of focusthat is substantially less than a thickness of the subject. An acquiredimage has a focused portion of the subject based on the distance. Thefocused portion is determined by the focal length and determined by thedepth of focus. For a particular sequence of acquired images, the methodincludes generating a synthetic image using the focused portions andincludes generating a distance image using the distances. The methodincludes generating a panoramic image using at least two syntheticimages and at least two distance images.

In one example, the method includes moving the subject relative to afixed location of the camera, and in one example, the method includesmoving the camera relative to a fixed location of the subject.Optionally, the method includes extracting a slice from an acquiredimage, and in one example, this includes calculating contrast. In oneexample, generating the distance image includes measuring a parameterusing convergent light beams. In one example, the method includesforming a two-dimensional representation of the subject.

One example includes a machine-readable medium having machine-executableinstructions for performing a method. The method includes acquiring aplurality of raw images for a subject in a volume. The raw images arespatially differentiated as to a distance between the subject and acamera. The raw images have a focused portion of the subject. The rawimages correspond to at least two radials about the volume. The camerahas a fixed focal length and a fixed depth of focus that issubstantially less than a thickness of the subject. The focused portionis determined by the focal length and determined by the depth of focus.The method includes generating a synthetic image for a particularradial. The synthetic image corresponds to a fusion of the focusedportions of the raw images of the particular radial. The method includesgenerating a distance image for the particular radial. The distanceimage corresponds to the distance of the focused portions of the rawimages of the particular radial. The method includes generating apanoramic image using the synthetic images and using the distanceimages.

In one example, the method includes controlling the distance between thesubject and the camera. In one example, the method includes controllinga position of the camera. Optionally, the method includes measuring aparameter using two convergent light beams. Optionally, the methodincludes measuring an illuminated region on the subject using twoconvergent light beams. In one example, generating the synthetic imageincludes calculating a measure of contrast. In one example, the methodincludes controlling an illumination source.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown and described.

Method examples described herein can be machine-implemented orcomputer-implemented at least in part. Some examples can include acomputer-readable medium or machine-readable medium encoded withinstructions operable to configure an electronic device to performmethods as described in the above examples. An implementation of suchmethods can include code, such as microcode, assembly language code, ahigher-level language code, or the like. Such code can includecomputer-readable instructions for performing various methods. The codemay form portions of computer program products. Further, the code may betangibly stored on one or more volatile or non-volatilecomputer-readable media during execution or at other times. Thesecomputer-readable media may include, but are not limited to, hard disks,removable magnetic disks, removable optical disks (e.g., compact disksand digital video disks), magnetic cassettes, memory cards or sticks,random access memories (RAMs), read only memories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the art,upon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims.

Also, in the above Detailed Description, various features may be groupedtogether to streamline the disclosure. This should not be interpreted asintending that an unclaimed disclosed feature is essential to any claim.Rather, inventive subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separate embodiment. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A system comprising: a plurality of cameras togenerate a plurality of raw images of a fingerprint in a volume, thecameras having a fixed focal length and a fixed depth of focussubstantially less than a thickness of the fingerprint and the camerasdirected along selected radials of the volume, wherein a distancebetween a camera and the fingerprint is variable, and wherein aparticular raw image includes a focused portion of the fingerprintcorresponding to the distance, the focused portion determined by thefocal length and determined by the depth of focus; and a processorcoupled to the cameras to execute a set of instructions to generate apanoramic image, the panoramic image based on a plurality of syntheticimages and based on a plurality of distance images, and wherein aparticular synthetic image includes a fusion of focused portions.
 2. Thesystem of claim 1 wherein at least one camera is stationary and thefingerprint is mobile.
 3. The system of claim 1 wherein at least onecamera is mobile and the fingerprint is stationary.
 4. The system ofclaim 1 wherein at least one camera is configured to generate a timeseries of raw images.
 5. The system of claim 1 wherein the processor isconfigured to generate a particular synthetic image using the raw imagesand a measure of contrast.
 6. The system of claim 1 wherein theprocessor is coupled to a communication network.
 7. A method comprising:for at least two radials from a volume, receiving a sequence of acquiredimages differentiated in a distance from a camera to a fingerprintwithin the volume, wherein the camera has a fixed focal length and afixed depth of focus substantially less than a thickness of thefingerprint, wherein a particular acquired image includes a focusedportion of the fingerprint based on the distance, the focused portiondetermined by the focal length and determined by the depth of focus; fora particular sequence of acquired images, generating a synthetic imageusing the focused portions and generating a distance image using thedistances; and generating a panoramic image using at least two syntheticimages and at least two distance images.
 8. The method of claim 7wherein receiving the sequence of acquired images differentiated in adistance from the camera to the fingerprint includes moving thefingerprint relative to a fixed location of the camera.
 9. The method ofclaim 7 wherein receiving the sequence of acquired images differentiatedin a distance from the camera to the fingerprint includes moving thecamera relative to a fixed location of the fingerprint.
 10. The methodof claim 7 wherein generating the synthetic image includes extracting aslice from a particular acquired image.
 11. The method of claim 10wherein extracting the slice includes calculating contrast.
 12. Themethod of claim 7 wherein generating the distance image includesmeasuring a parameter using convergent light beams.
 13. The method ofclaim 7 wherein generating the panoramic image includes forming atwo-dimensional representation of the fingerprint.
 14. Amachine-readable memory device having machine-executable instructionsfor performing a method comprising: acquiring a plurality of raw imagesfor a fingerprint in a volume, the raw images spatially differentiatedas to a distance between the fingerprint and a camera and the raw imageshaving a focused portion of the fingerprint, the raw imagescorresponding to at least two radials about the volume and the camerahaving a fixed focal length and a fixed depth of focus substantiallyless than a thickness of the fingerprint, the focused portion determinedby the focal length and determined by the depth of focus; generating asynthetic image for a particular radial, the synthetic imagecorresponding to a fusion of the focused portions of the raw images ofthe particular radial; generating a distance image for the particularradial, the distance image corresponding to the distance of the focusedportions of the raw images of the particular radial; and generating apanoramic image using the synthetic images and using the distanceimages.
 15. The machine-readable memory device of claim 14 wherein themethod includes controlling the distance between the fingerprint and thecamera.
 16. The machine-readable memory device of claim 14 wherein themethod includes controlling a position of the camera.
 17. Themachine-readable memory device of claim 14 wherein generating thedistance image includes measuring a parameter using two convergent lightbeams.
 18. The machine-readable memory device of claim 14 whereingenerating the distance image includes measuring an illuminated regionon the fingerprint using two convergent light beams.
 19. Themachine-readable memory device of claim 14 wherein generating thesynthetic image includes calculating a measure of contrast.
 20. Themachine-readable memory device of claim 14 wherein acquiring theplurality of raw images includes controlling an illumination source.